1. Field of the Invention
The invention relates to a method for the optimization of a conductor-path layout for a print head in an ink jet printers as well as a conductor-path layout for such a print head, wherein a plurality of heating elements is selectively controlled via conductor paths, and wherein the conductor paths are distributed on a thin-film substrate to a terminal connector field.
2. Brief Description of the Background of the Invention Including Prior Art
The uniformity in heating capability of the heating resisters as well as of feed line resisters have to be assured in the high resolution ink print devices operating according to the bubble jet principle. Otherwise, the volumes of heat, generated in various heating elements of a print head, vary under certain circumstances such that some heating elements are overloaded. This can result in the reduction of the life time of a print head or also in a reduction of the maximum operating frequency by uncontrolled evaporation processes in the ink. In case of known thin-film layouts for such print heads, each individual heating element comprises its own electrical feed and return line in the structure of the metallic conductor paths, preferably made of aluminum which, for the purpose of an external electrical contacting, are distributed at individual conductors of a connection cable via the area of the thin-film substrate, and are led to a connector terminal field.
The electrical resistance of the feed lines i.e. of a feed line and of a return line, of the heating element is usually about RZ=20 .OMEGA. and cannot be neglected any longer as compared to the resistance of the heating element itself with RH equal to about 80 .OMEGA..
Since the heating elements are disposed in a near-edge region of the thin-film substrate in one row with narrow subdivision, and since the feed lines have to be led on the opposite side of the thin-film substrate for the purpose of forming a contact to the relatively wide connection field, there result also different feed line resistances for the individual heating elements based on the different lengths of the conductors, which leads to the above recited problems.
Conductor path layouts for the individual connection of heating elements are known from the Japanese Patent documents JP-A-61-2,575 and JP-A-60-76,355. These references teach that the connection lines, starting from the heating elements to be contacted, are subdivided into a region with wide spacing, into a region with close spacing, where this region adjoins a connection of an integrated circuit, and into a transition region connecting the two aforementioned regions. The connection lines run parallel to each other in these individual regions and, in order to achieve a substantially equal feed-in resistance of the individual connection lines, resistance correction zones are provided either only on one side at the heating elements to be contacted, as taught in the Japanese Patent document JP-A-60-76,355, or on both sides of the heating elements as taught in the Japanese Patent document JP-A-61-2,575. The correction zones and the line resistance compensation paths are therefore provided in the regions of wide spacing by sections of differing width and length of the connection lines alone.